Advancing blades of a surgical retractor through an incision and into position adjacent a surgical site involves overcoming resistance from muscles, tendons, and other tissues within the body. When the surgical retractor is used to access a patient's spine from the side of the patient, known as lateral approach surgery, the distance to the patient's spine is greater than if the spine were accessed through the patient's back, known as posterior approach surgery. The increased distance to the spine during lateral approach surgery means overcoming a greater amount of resistance from muscles, tendons, and other tissues in order to advance the retractor blades to the surgical site than in a posterior approach surgery.
Another difficulty with lateral approach surgery is that the tissues surrounding the retractor blades tightly envelop and deflect the blades as the blades are slid along a dilator toward the surgical site. The increased distance to the spine for lateral approach surgery means that the retractor blades must be longer in order to retract tissues adjacent the surgical site. Like cantilever beams, the longer retractor blades used for lateral approach surgery are subjected to forces from the surrounding tissues that deflect the blades a greater amount than if the blades were shorter blades typically used for posterior approach surgery. Deflection of the long retractor blades allows the tissues enveloping the blades to lodge between the blades and the dilator as well as creep into gaps between the blades. The retractor blades may have to be removed and re-inserted into the patient to remove tissues caught between the blades and the dilator or caught in gaps between the blades, which complicates the surgical procedure.
For longer length blades, such as the 80 mm-180 mm blades typically used for lateral approach surgery, small manufacturing variations in straightness along the blades are magnified by the length of the blades. These variations are problematic, as even a slight curvature may cause the tip of a longer blade to lift up from the dilator and trap tissue as the blade is advanced toward the surgical site. Variations in blade straightness may also cause the tips of the retractor blades to be unevenly spaced around the dilator and permit tissue creep between the retractor blades. These situations increase the difficulty of advancing the retractor blades toward the surgical site and complicate the process of establishing a working channel to the spine.